Vitamin D not behind UVB's psoriasis benefit

NEW YORK (Reuters Health) - Ultraviolet light therapy lessens the symptoms of psoriasis and simultaneously raises vitamin D levels, a new study shows. However, increased vitamin D is probably unrelated to light therapy's benefits for psoriasis, the researchers say.

Psoriasis is a chronic skin condition that leaves up to 3 percent of the population with patches of thick, itchy and sometimes painful red skin. Abnormalities in vitamin D metabolism may be partly to blame for the development and worsening of psoriasis.

Many psoriasis sufferers seek light therapy, the standard of which is narrowband ultraviolet B (UVB) light therapy, which mimics the portion of the sun's invisible light rays known to trigger the skin's production of vitamin D.

Because previous research in people with psoriasis has shown that this treatment raises levels of vitamin D and improves the skin condition, Dr. Caitriona Ryan and her colleagues at St. Vincent's University Hospital in Dublin, Ireland, wondered if these benefits might be linked.

To investigate, they followed 60 psoriasis patients during an Irish winter -- between October 2008 and February 2009. Half were treated with UVB light therapy three times a week until their psoriasis cleared; the others received no light therapy. Vitamin D levels in the blood were measured along the way.

The researchers found that the average patient undergoing UVB light therapy more than doubled their blood levels of vitamin D by the end of the treatment period, which most completed in about 50 days. All of them reached vitamin D sufficient levels, the researchers report in the Archives of Dermatology.

As expected, psoriasis also significantly improved with UVB light therapy. Half the patients started out with psoriasis severity scores above 7.1, and by the end of treatment half had scores of 0.5 or below.

In contrast, three out of every four patients not receiving light therapy remained vitamin D insufficient at the end of the study. They also experienced no overall improvement in psoriasis severity.

When the researchers analyzed the levels of vitamin D and the extent of psoriasis relief, however, they could find no association between the two.

"The improvement in both vitamin D status and psoriasis may be contemporaneous, but unrelated, consequences" of UVB light therapy, Ryan told Reuters Health in an email.

This finding came as no surprise to Dr. Leon Kircik of Indiana University in Indianapolis.

"Any vitamin D in the blood is not going to help psoriasis. You need it on the skin," he told Reuters Health, pointing to topical vitamin D as an effective psoriasis treatment.

Still, he noted that UVB light therapy is one of the best and safest options for combating psoriasis. So far, it has not been shown to increase the risk of skin cancer, he said, "and it's been used for a long time, even for pregnant women."

But Dr. Amra Osmancevic of the University of Gothenburg in Sweden cautions that UVB light therapy remains a known human carcinogen. Its intentional use in healthy people to only induce vitamin D production is not recommended, Osmancevic told Reuters Health in an email.